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Energy crops have proved to be a viable alternative to fossil fuels. However, high biomass production always means that large quantities of nutrients from the soil are removed at harvest. The goal of this work was to estimate nutrient (nitrogen, phosphorous, potassium) use efficiency (NUE) and nitrogen balance in an eight-year-old Populus deltoides clone Lux, short rotation forestry under two cutting cycles, every two (biennial) and three (triennial) years, carried out under Mediterranean climate conditions. Results indicate that NUE, for all the analyzed elements, contained variations with slightly higher values for nitrogen and phosphorous in the triennial cycle. Although poplar cultivation has a positive nutrient efficiency, in terms of nitrogen, there is significant loss of this element in the crop cycle. [ABSTRACT FROM AUTHOR]

Perennial crops can positively act on the environment providing a better inter-annual protection of soil cover from water erosion, limiting soil fertility degradation, the risk of nutrient leaching and the exploitation of water for irrigation. Switchgrass (Panicum virgatum L.), a warm-season grass native from North America, has been cultivated for decades as forage crop and only recently as bioenergy crop. Even if several studies reported a positive effect of nitrogen (N) supply on switchgrass yield and quality, potential indirect and direct environmental risks (e.g., eutrophication and greenhouse gas emission) are related to this practice. For this reason grass-legume intercropping can represent a sustainable practice able to increase biomass yield and quality, and at the same time to improve N use efficiency, soil structure and fertility. Based on this, the aim of this study was to evaluate the suitability of switchgrass to Mediterranean environment as forage crop and to improve biomass yield and its nutritional value by intercropping with alfalfa (Medicago sativa L). During spring 2013, in two switchgrass pure stands (varieties Alamo and Blackwell, respectively), alfalfa was established through direct seeding implementing a split-plot experimental design. Our first year results report a positive effect of the intercropping in increasing the total annual yield of the stand, of about 20% with respect to the pure switchgrass stand. However, the presence of alfalfa negatively affected switchgrass yield in the mixture. In both varieties, the crude protein content was higher in the mixture than in the pure switchgrass stands. Conversely, the neutral detergent fibre content in the mixture was lower than in pure switchgrass. Then, our results show that switchgrass-alfalfa intercropping leads to increase the profitability of grassland-based livestock production. [ABSTRACT FROM AUTHOR]

Biomass productivity is the main favorable trait of candidate bioenergy crops. Miscanthus × giganteus is a promising species, due to its high-yield potential and positive traits including low nutrient requirements and potential for C sequestration in soils. However, miscanthus productivity appears to be mostly related to water availability in the soil. This is important, particularly in Mediterranean regions where the risk of summer droughts is high. To date, there have been no studies on miscanthus responses under different soil conditions, while only a few have investigated the role of different crop managements, such as irrigation and nitrogen fertilization, in the Mediterranean. Therefore, the effects of contrasting soil textures (i.e. silty-clay-loam vs. sandy-loam) and alternative agricultural intensification regimes (i.e. rainfed vs. irrigated and 0, 50, 100 kg ha−1 nitrogen fertilization), on miscanthus productivity were evaluated at three different harvest times for two consecutive years. Our results confirmed the importance of water availability in determining satisfactory yields in Mediterranean environments, and how soil and site characteristics strongly affect biomass production. We found that the aboveground dry yields varied between 5 Mg ha−1 up to 29 Mg ha−1. Conversely, nitrogen fertilization played only a minor role on crop productivity, and high fertilization levels were relatively inefficient. Finally, a marked decrease, of up to −40%, in the aboveground yield occurred when the harvest time was delayed from autumn to winter. Overall, our results highlighted the importance of determining crop responses on a site-by-site basis, and that decisions on the optimal harvest time should be driven by the biomass end use and other long-term considerations, such as yield stability and the maintenance of soil fertility. [ABSTRACT FROM AUTHOR]

Cropping among trees with perennial legumes is one option for increasing agro-ecosystem services, such as improving the nitrogen supply and increasing soil protection by herbaceous vegetation. Moreover, cropping under the canopy of olive trees should diversify the farm production, compared to the traditional fallow management. Among perennial legumes, alfalfa (Medicago sativa L.) produces abundant biomass under Mediterranean rainfed condition. Based on this, a two-year field experiment was implemented in southern Tuscany in a rainfed olive orchard to test the competition for light effects on alfalfa biomass production and nutritive value. Light availability under the tree canopy was measured by hemispherical photos. In both years, the alfalfa yield of under-canopy varied according to the tree presence. A significant relationship between biomass production and light availability was recorded. The nutritive value of under-canopy alfalfa was similar to that of the open-grown alfalfa. However, same significant differences did however occur, between shaded and sole crop. When differences were found, under-canopy herbage was characterised by a higher content of crude protein and a lower content of fibre with respect to open-grown. In a hilly silvoarable olive orchard, alfalfa biomass accumulation was reduced mainly due to scarce light availability, therefore tree management such as pruning and plantation layout can enhance the herbage productivity. Studying shade tolerant forage legumes in order to enhance the yield and nutritive value of herbage production in rainfed agroforestry systems is essential. [ABSTRACT FROM AUTHOR]

Limits in propagation are hampering the diffusion of giant reed cultivation for biomass. The objective of this study was to compare rhizomes and micropropagated plants with stem cuttings obtained in spring vs late winter (with and without side shoots, respectively) and immediately planted. A three-years field trial was carried out, assessing how rapidly giant reed establishes, and how its yield components (i.e. crop height, stem density, stem diameter) and its rhizomes develop over years depending on the propagation method adopted. Long-lasting variations in yield components depending on propagation were found. In the three years, biomass yield was steadily higher in rhizome-propagated stands (+64% than the average of the other propagation materials), while no significant interactions with the year of study were observed. Stems were thicker in rhizome-propagated and thinner in micropropagated plants, while cutting-propagated ones showed intermediate values. Micropropagation led to a significantly lower ratio between the biomass of rhizomes and the number of rhizome buds. Moreover, micropropagated plants were shorter (crop height: 34%), while stem density was nearly doubled: an inverse relationship between tillering and elongation was highlighted. Plants obtained from winter cuttings were taller than those obtained in spring, although the height difference was mostly achieved towards the end of the vegetative season. At initial growth stages, winter cuttings were slower than spring cuttings in increasing sprout density. Immediately-planted cuttings showed potential to replace micropropagated plants. In particular, cuttings obtained in spring , showed suitability for on-farm propagation, by means of collection from existing stands followed by direct planting. • Long lasting inverse relationship between stem density and elongation was found. • Micropropagation led to lower ratio between rhizome biomass and rhizome buds. • Rhizomes produced thicker stems, stem cuttings generally showed intermediate values. • Winter cuttings were slower than spring cuttings in increasing sprout density at initial stages. • Immediately-planted cuttings showed potential to replace micropropagated plants. [ABSTRACT FROM AUTHOR]